Anomalous temperature and salinity variations in the tropical Atlantic: Possible causes and implications for the use of altimeter data

Near real time subsurface observations at a PIRATA mooring in the western equatorial Atlantic show a temperature and salinity drop in boreal spring 1999 which is consistent with a 60 m upward shift of the thermocline. At the same time, sea level observations from TOPEX/Poseidon and ERS‐1/2 show anomalously low values over a large part of the tropical Atlantic north of the equator. The sea level observations are also used to correct for errors in upper ocean heat content in a global ocean analysis, which is used to initialize seasonal forecasts. It is shown that the ability of altimeter data to reproduce observed temperature changes is limited in the western equatorial Atlantic. This may partly be because large temperature changes occur very rapidly, but is mainly because strong salinity variations compensate up to 10 cm of the sea level signal from temperature.